Mitochondrial DNA Fragmentation to Monitor Safety and Quality in Roasted Peanuts

Abstract

ABSTRACT Mitochondrial DNA (mtDNA) fragmentation has been proposed as a time-temperature integrator (TTI) for high-moisture thermal processes using low-acid, high-temperature and high-acid, low-temperature protocols. In this study, dry roasted peanuts were assayed using the same novel molecular TTI. Enterococcus faecium was evaluated as a Salmonella surrogate for process validation and compared to fragmentation of intrinsic peanut mtDNA and Hunter L color, a quality indicator, for dry roasting. Reduction curve data for E. faecium were highly repeatable as similar kinetics were observed when compared to another study which used a commercial, contract laboratory to validate this same surrogate for use with dry roasted peanuts processes (4-log reduction after 10 min at 167 C). Mitochondrial DNA fragmentation was not linear compared to time at a given temperature, but exhibited a long lag time. D and z-values were calculated using E. faecium, threshold cycle (Ct) and Hunter L color values. D values for E. faecium were 2.68, 2.06 and 1.89 min for 138, 153 and 167 C roasting temperatures, respectively. Mitochondrial DNA fragmentation as measured by Ct had a D value of 12.3 min at a roasting temperature of 167 C which was slightly higher than “wet” processes (ca. 11.5 min). Hunter L values had an inverse, linear relationship with time at a given temperature. Hunter L color, if applied to individual peanuts and empirically validated, could be used as an inexpensive visible method to troubleshoot continuous flow systems. Ct values were not linear or highly correlated to Hunter L values. Dissection of peanuts exhibited a differential heating effect depending on the part of the peanut used for DNA extraction and the type of tissue assayed. Mitochondrial DNA fragmentation as measured by Ct value was deemed too variable for thermal process or quality validation of dry, solid foods such as peanuts. However, it could be used to evaluate penetration of heat through a solid food matrix, to find the coldest spot and test the worst-case scenario.